The sternocleidomastoid originates from which structures?

• A. Top of the manubrium, medial one-third of the clavicle
• B. Mastoid process
• C. Occipital bone
• D. Zygomatic arch

Answer: (A)

The main idea here is understanding where the sternocleidomastoid attaches at its origin. This muscle has two heads: the sternal head and the clavicular head. The sternal head originates from the upper part of the manubrium of the sternum, and the clavicular head originates from the medial third of the clavicle. Together, these two origins match the description of coming from the top of the manubrium and the medial clavicle. The other structures listed aren’t origins for this muscle: the mastoid process is where the muscle inserts, not where it begins; the occipital bone and zygomatic arch aren’t sources of attachment for the sternocleidomastoid.